Azuma Yumiko, Ishikawa Yuji, Kawai Shigeto, Tsunenari Toshiaki, Tsunoda Hiroyuki, Igawa Tomoyuki, Iida Shin-ichiro, Nanami Masahiko, Suzuki Masami, Irie Reiko F, Tsuchiya Masayuki, Yamada-Okabe Hisafumi
Pharmaceutical Research Department III, Kamakura Research Laboratories, Chugai Pharmaceutical Co., Ltd., Kanagawa, Japan.
Clin Cancer Res. 2007 May 1;13(9):2745-50. doi: 10.1158/1078-0432.CCR-06-2919.
L612, a human IgM monoclonal antibody produced by an EBV-transformed human B-cell line, binds to ganglioside GM3 and kills GM3-positive human melanoma cells in the presence of complement. It has been shown to be effective in some patients with late-stage melanoma. L612 consists of hexameric IgM (about 20%), pentameric IgM (about 74%), and other minor IgM molecules. Because hexameric IgM activates complement more effectively than pentameric IgM, we developed and evaluated a hexamer-dominant recombinant IgM for clinical applications.
Chinese hamster ovary (CHO) cells were transfected with heavy- and light-chain genes of L612, with or without the joining-chain gene. Antitumor effects of the recombinant IgM secreted from CHO cells were evaluated in vitro and in vivo.
Recombinant IgM secreted from CHO cells without the joining chain (designated CA19) was approximately 80% hexameric, whereas recombinant IgM from CHO cells transfected with heavy-, light-, and joining-chain genes (designated CJ45) was about 90% pentameric. Both CA19 and CJ45 recombinant IgMs caused complement-dependent cytotoxicity against human and mouse melanoma cell lines, but the amount of CA19 required for 50% specific cytotoxicity was 5 to 10 times smaller. I.v. injection of CA19 compared with CJ45 or native L612 elicited more profound antitumor activity in nude rats bearing a GM3-positive mouse melanoma xenograft.
A hexamer-dominant human IgM against GM3 may provide a more potent treatment option for patients with GM3-positive melanoma.
L612是一种由EBV转化的人B细胞系产生的人IgM单克隆抗体，它与神经节苷脂GM3结合，并在补体存在的情况下杀死GM3阳性的人黑色素瘤细胞。已证明它对一些晚期黑色素瘤患者有效。L612由六聚体IgM（约20%）、五聚体IgM（约74%）和其他少量IgM分子组成。由于六聚体IgM比五聚体IgM更有效地激活补体，我们开发并评估了一种以六聚体为主的重组IgM用于临床应用。
用L612的重链和轻链基因转染中国仓鼠卵巢（CHO）细胞，转染时有的带有连接链基因，有的没有。对CHO细胞分泌的重组IgM的抗肿瘤作用进行体外和体内评估。
未转染连接链基因的CHO细胞分泌的重组IgM（命名为CA19）约80%为六聚体，而转染了重链、轻链和连接链基因的CHO细胞分泌的重组IgM（命名为CJ45）约90%为五聚体。CA19和CJ45重组IgM均对人和小鼠黑色素瘤细胞系产生补体依赖性细胞毒性，但产生50%特异性细胞毒性所需的CA19量要小5至10倍。与CJ45或天然L612相比，静脉注射CA19在携带GM3阳性小鼠黑色素瘤异种移植瘤的裸鼠中引发了更强的抗肿瘤活性。
一种以六聚体为主的抗GM3人IgM可能为GM3阳性黑色素瘤患者提供更有效的治疗选择。
